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United States Patent |
5,652,509
|
Weis
|
July 29, 1997
|
Device for determining the velocity of a longitudinally traveling
elongate textile material, especially a yarn, using electronic sensors
Abstract
A device for determining the velocity of a longitudinally traveling textile
material, especially a yarn, using the closed-loop correlation of a
transit time correlator in such a way that its reliability is improved. At
least one sensor g.sub.1 consists of two signal receivers disposed one
behind the other in the running direction of the yarn, having a sensor
output characteristic curve with the intersection of the abscissa in the
effective sensor center axis, and wherein the output characteristic curve
shows a point-symmetrical behavior at least in the vicinity of the
intersection with the abscissa. A second sensor g.sub.2 has a steady state
output characteristic curve in the area of its effective sensor center
axis. The control loop circuit of the transit time correlator is designed
such that the undifferentiated cross-correlation function is used as the
controller input signal for determining and readjusting the adjustment
point for the model delay time .tau.. Optionally, the output
characteristic curves of the sensors have amplified outputs. The
determination of the adjustment point and the stability of the control
loop circuit can be further improved by the use of a third sensor with an
output characteristic curve corresponding to that of the second sensor,
and of a fourth sensor for providing a range preselection for the
feed-back integrator of the transit time correlator.
Inventors:
|
Weis; Manfred (St. Wendel, DE)
|
Assignee:
|
W. Schlafhorst AG & Co. (Moenchengladbach, DE)
|
Appl. No.:
|
533071 |
Filed:
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September 25, 1995 |
Foreign Application Priority Data
| Sep 24, 1994[DE] | 44 34 234.9 |
Current U.S. Class: |
324/175; 324/178; 356/28 |
Intern'l Class: |
G01P 003/36; G01P 003/80; B65H 059/38; B65H 063/00 |
Field of Search: |
324/175,178,206,658,663
356/28
250/215,216,571
|
References Cited
Foreign Patent Documents |
0 000 721 A1 | Jul., 1977 | EP.
| |
0 582 112 A1 | Aug., 1992 | EP.
| |
19 22 461 | Apr., 1969 | DE.
| |
25 44 819 A1 | Apr., 1977 | DE.
| |
42 25 842 A1 | Feb., 1994 | DE.
| |
1321 | Dec., 1991 | JP.
| |
669 777 A5 | Apr., 1989 | CH.
| |
Other References
Prof. Dr.-Ing. habil. Roland Backmann et al, "Beruhrungslose
Geschwindigkeitsmessung am laufenden Faden," Melliand Textilberichte,
Jul./1993, 639-40.
Werner Ringens et al, "Optoelektronischer Sensor zur beruhrungslosen
Geschwindigkeitsmessung an textilen Oberflachen," Textil Praxis
International, Jun. 1988.
|
Primary Examiner: Snow; Walter E.
Attorney, Agent or Firm: Shefte, Pinckney & Sawyer
Claims
What is claimed is:
1. In a device for determining the velocity of an elongate textile
material, in particular a textile yarn, traveling longitudinally in its
lengthwise dimension, wherein two sensors are disposed at a predetermined
distance L along the direction of traveling movement of the textile yarn
which produce measured sensor signals which are evaluated using a transit
time correlator having a control loop circuit adjusted to a model delay
time .tau. which corresponds to an actual transit time T of a yarn segment
over the predetermined distance L, and that the velocity is calculated by
a dividing circuit element connected to the control loop circuit of the
transit time correlator, for obtaining a quotient from the predetermined
distance and the model delay time, the improvement comprising:
a first sensor g.sub.1 of said two sensors including at least two signal
receivers (1,2; 5,6; 9,10; 17,18; 25,26,27,28) disposed in sequence along
the travel direction of the yarn, said first sensor g.sub.1 having a
sensor output characteristic curve which intersects the abscissa,
indicating a zero instantaneous output value, in the effective sensor
center axis, and wherein said output characteristic curve shows a
point-symmetrical behavior at least in the vicinity of the intersection
with the abscissa;
a second sensor g.sub.2 of said two sensors having a steady state output
characteristic curve waveform in the area of its effective sensor center
axis; and
the control loop circuit for the transit time correlator includes means for
using an undifferentiated cross-correlation function as the controller
input signal for determining and readjusting an adjustment point for the
model delay time .tau..
2. A device for determining the velocity of an elongate textile material
according to claim 1 wherein said first sensor g.sub.1 has a
point-symmetrical output characteristic curve.
3. A device for determining the velocity of an elongate textile material
according to claim 1 or 2 wherein the second sensor g.sub.2 has an output
characteristic curve which is symmetrical in respect to a sensor center
axis associated with said second sensor g.sub.2.
4. A device for determining the velocity of an elongate textile material
according to claim 1 wherein the output characteristic curve of the second
sensor g.sub.2 displays a balanced output.
5. A device for determining the velocity of an elongate textile material
according to claim 1 wherein the output characteristic curve of the first
sensor g.sub.1 displays a balanced output.
6. A device for determining the velocity of an elongate textile material
according to claim 1 wherein said first sensor g.sub.1 and said second
sensor g have output characteristic curves such that by imaginarily
shifting one of the sensors by a predetermined amount equal to the
effective distance L between the center axes of said first sensor and said
second sensor in the direction toward the other sensor, the respective
sensor output characteristic curves are periodic functions with a phase
difference of 90.degree..
7. A device for determining the velocity of an elongate textile material
according to claim 1 wherein said first sensor and said second sensor have
output characteristic curves having a square waveform.
8. A device for determining the velocity of an elongate textile material
according to claim 1 and further comprising a third sensor g.sub.3 having
an output characteristic curve the same as that of the second sensor
g.sub.2 and is disposed within said device at a position wherein an
effective sensor center axis associated with said third sensor g.sub.3 is
coincident with an effective center axis associated with said first sensor
g.sub.1.
9. A device for determining the velocity of an elongate textile material
according to claim 8 and further comprising a summation circuit for
determining a difference between a second sensor signal s.sub.2 and a
third sensor signal s.sub.3 and for forming a difference signal which is
used with a first sensor signal for forming the cross-correlation function
used as the controller input signal.
10. A device for determining the velocity of an elongate textile material
according to claim 1 wherein a distance L between said first sensor
g.sub.1 and said second sensor g.sub.2 is such that a minimum or maximum
value of the sensor correlation function R.sub.g1g2, which adjoins the
intersection of the sensor correlation function R.sub.g1g2 derived from
the product of the sensor output characteristic curves with the abscissa,
lies on the ordinate.
11. A device for determining the velocity of an elongate textile material
according to claim 1 and further comprising a signal emitter g.sub.4 which
transmits velocity signals s.sub.4 which are proportional to the yarn
velocity, and signals s.sub.4 from the signal emitter g.sub.4 can be
provided to the transit time correlator for range preselection for lock-on
of the control loop circuit on a real intersection of the
cross-correlation function .PHI.(.tau.) with the abscissa.
Description
FIELD OF THE INVENTION
The present invention relates to a device for determining the velocity of
an elongate textile material, in particular a textile yarn, traveling in
longitudinally in its lengthwise dimension, wherein two sensors disposed
at a predetermined spacing along the direction of traveling movement of
the textile yarn produce measured sensor signals which are evaluated using
a transit time correlator having a control loop circuit adjusted to a
model delay time which corresponds to the actual transit time of a yarn
section over the distance and the traveling velocity is calculated by a
dividing element connected to the control loop circuit of the transit time
correlator for determining a quotient, representing yarn velocity, from
the distance and the model delay time.
BACKGROUND OF THE INVENTION
Many textile machines wherein textile yarns travel longitudinally along
their length to be subsequently wound require a device for monitoring the
velocity or the length of the traveling textile yarn then wound. The
result is used, for example, to correct deviations in velocity and to
obtain as accurate as possible information regarding the length of the
yarn which has been wound as of any given time.
For example, in connection with bobbin winding machines producing
cheese-type bobbins, or yarn packages, there is often a requirement that
all produced bobbins have exactly the same yarn length if possible. This
is primarily necessary if these bobbins are to be subsequently placed on a
creel and drawn off together to form a warp beam. Different yarn lengths
lead to residual yarn of different lengths on the bobbin tubes in such a
case. With yarn material of high quality this results in unacceptable, and
possibly costly losses.
A widely used method to determine the yarn length on such bobbin winding
machines is to count the revolutions of the bobbin or of the drive roller
for the bobbin and to determine the wound-on amount of yarn using
calculations based on the circumference of the bobbin or of the drive
roller for the bobbin. Since the circumference of the drive roller is
constant, the determination of the circumferential velocity poses no
problems. Nevertheless, the slippage which typically occurs between the
drive roller and the bobbin can be a considerable source of errors. The
resultant calculated velocity or yarn length value may be greatly
distorted since, to avoid so-called "pattern winding," a slippage between
the drive roller and the bobbin is intentionally generated during the
entire bobbin travel or at least in so-called pattern zones in which the
bobbin diameter and the diameter of the drive roller have a defined
relationship to each other.
Measuring the number of bobbin revolutions is relatively simple. However,
the exact determination of the progressively changing diameter (and in
turn the bobbin circumference) occurring during the course of bobbin
winding can be problematical. If the angle of rotation of the bobbin
support is used as the measurement for the bobbin radius, considerable
errors can also result because of deviations in the pressure of the bobbin
on the drive roller.
A number of methods are known for determining the yarn velocity by contact
with the yarn. Such a method increases the yarn tension and is unsuitable
for higher re-spooling velocities because of the inertia of the element
which is moved along with the yarn.
To avoid the mentioned disadvantages it has been proposed in European
Patent Publication EP 0 000 721 A1 to determine the yarn velocity by means
of two contactless operating sensors placed at a fixed distance from each
other. Optically or capacitively operating sensors, for example, are
suited for this purpose. These sensors determine stochastic yarn signals
in the form of analog noise signals resulting from irregularities of the
yarn surface or yarn mass in the longitudinal direction of the traveling
yarn. The stochastic signal detected upstream in the direction of travel
is temporally displaced sufficiently far until it shows a maximal
similarity with the stochastic signal detected at the sensor placed
downstream, indicating the time delay existing between the two signals.
The delay of the first signal determined in the course of this operation
corresponds to the length of time the yarn requires to travel from the
first to the second sensor. Since the distance between the two sensors is
known, it is possible in this way to easily determine the yarn velocity.
However, the mathematical operations, which are customarily called a
cross-correlation method, are subject to a certain expenditure of time.
This poses no problems if the yarn is subjected to no or only very small
accelerations. However, more rapid velocity changes, such as those which
occur in the winding process because of common patterning disturbances,
for example, cannot be handled in such a way that an exact measurement can
take place. Since differentiation of the cross-correlation function is
required for determining the primary maximum of this function, the
measured value data scatter increases with low signals in relation to the
noise acting as an interference value.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved
device and method for measuring the velocity of a traveling textile
material with a high degree of accuracy.
To that end, a device for determining the velocity of an elongate textile
material, in particular a textile yarn, traveling longitudinally in its
lengthwise dimension, is disclosed wherein two sensors are disposed at a
predetermined distance along the direction of traveling movement of the
textile yarn which produce measured sensor signals which are evaluated
using a transit time correlator having a control loop circuit adjusted to
a model delay time which corresponds to an actual transit time of a yarn
segment over the predetermined distance, and that the velocity is
calculated by a dividing circuit element connected to the control loop
circuit of the transit time correlator, for obtaining a quotient from the
predetermined distance and the model delay time. The velocity
determination device according to the present invention includes at least
one first sensor g.sub.1 including at least two signal receivers (1,2;
5,6; 9,10; 17,18; 25,26,27,28) disposed in sequence along the travel
direction of the yarn, the first sensor g.sub.1 having a sensor output
characteristic curve which intersects the abscissa, indicating a zero
instantaneous output value, on the effective sensor center axis, and
wherein said output characteristic curve shows a point-symmetrical
behavior at least in the vicinity of the intersection with the abscissa.
Further, the present invention includes a second sensor g.sub.2 having a
steady state output characteristic curve waveform in the area of its
effective sensor center axis, and a control loop circuit for the transit
time correlator that includes means for using an undifferentiated
cross-correlation function as the controller input signal for determining
and readjusting an adjustment point for the model delay time .tau..
In contrast to the known use of a transit time correlator based on a closed
loop correlation, a differentiation of the cross-correlation function is
no longer required with the present invention. In the process, a
point-symmetrical (at least in the vicinity of the adjustment point)
function is employed for determining the adjustment point which utilizes
the main advantage of the closed loop correlation over the open loop
correlation. The adjustment point which results with a time displacement
over a model delay time .tau., which corresponds to the actual transit
time T of a yarn section over the distance L between two sensors, is
located on the intersection of the cross-correlation function with the
abscissa, in other words, the minimum value of the cross correlation
function. The calculation effort and the measured value data scatter
associated with a low signal is reduced in respect to the noise conditions
and to the sensitivity to interference signals as a whole because of the
omission of the differentiation in relation to a transit time correlator
on the basis of the known closed loop correlation. In addition, this
results in the advantage that the transit time estimate or the
determination of the adjustment point can take place to a great extent by
means of linear averaging over a velocity range.
Assuming that the temporal cross-correlation function .PHI.(.tau.) is
formed by superposition of the sensor correlation function R.sub.g1g2 with
the local auto-correlation function of the inhomogeneities of the material
to be measured, a rounding of the corners of a plot of the
cross-correlation function .PHI.(.tau.) in respect to the sensor
correlation function R.sub.g1g2 results, caused by the texture of the
textile material to be measured. The slope of the cross-correlation
function as a whole, but also in the range of the adjusting point,
increases with an increasing critical frequency of the texture. This
dependency of the slope of the cross-correlation function is, however,
considerably less than with the known closed loop correlation. This has
very advantageous results on the stability of the control loop circuit in
relation to changing textures, because the changes in the slope of the
correlation function directly result in a proportional change of the loop
amplification of the adjustment control loop circuit.
It is preferred that the first sensor g.sub.1 has a point-symmetrical
output characteristic curve. It is further preferred that the second
sensor g.sub.2 has an output characteristic curve which is symmetrical in
respect to its sensor center axis.
The combination of output signals resulting from the use of a first sensor
g.sub.1 having a point-symmetrical output characteristic curve, such as a
square wave, and of a second sensor g.sub.2 having an output
characteristic curve symmetrical in relation to its respective sensor
central axis results in a point-symmetrical sensor correlation function
R.sub.g1g2 and therefore also in a point-symmetrical cross-correlation
function .PHI.(.tau.) over the entire waveform. This results in the
suppression of systematic errors even at greater velocity fluctuations.
Preferably, the second sensor g.sub.2 has an output characteristic curve
that displays a balanced output. Similarly, the first sensor g.sub.1 may
have an output characteristic curve of the first sensor g.sub.1 displays a
balanced output. When using sensors with characteristic curves having a
balanced output, sensor signals S.sub.1 (t) and S.sub.1 (t) free of mean
values result, so that it is possible to omit a high-pass filter which
otherwise is generally required in the signal field. This applies in
particular if the signal should be clipped prior to further processing.
The first sensor g.sub.1 and the second sensor g.sub.2 preferably have
output characteristic curves such that by shifting one of the sensors by a
predetermined amount equal to the effective distance L between the center
axes of the first sensor and the second sensor in the direction toward the
other sensor, the respective sensor output characteristic curves are
periodic functions having a phase difference of 90.degree.. The behavior
of the sensor output characteristic curves as periodic functions with a
phase difference of 90.degree. provides a sensor correlation function with
periodic behavior resulting therefrom which is point-symmetrical in
relation to the adjustment point.
The sensors g.sub.1, g.sub.2 preferably have output characteristic curves
having a square waveform. It is not difficult to obtain sensors having
sensor output characteristic curves with a square waveform by means of a
diode-based circuit. This also results in sensor correlation functions
with a linear path between two respectively adjoining extreme points, but
at least between the intersection points with the abscissa, or zero value
points, and the adjoining extreme, or maximum value points. This further
simplifies the evaluation.
A third sensor g.sub.3 having an output characteristic curve similar to
that of the second sensor g.sub.2 is disposed within said device such that
its effective sensor center axis is coincident with the effective center
axis of the first sensor g.sub.1. The employment of a third sensor g.sub.3
with an output characteristic curve coincident with that of the second
sensor g.sub.2 reduces the scattering of transit time estimated values. In
this case the control input signal becomes zero if .tau.=T. As a result
the scattering of the transit time estimate disappears if no interference
signals are present.
A summation circuit is provided for determining a difference between a
second sensor signal S.sub.2 and a third sensor signal S.sub.3, and for
forming a difference signal which is used with a first sensor signal for
forming the cross-correlation function used as the controller input
signal.
Further, the first sensor g.sub.1 and second sensors g.sub.2 may be
arranged such that a distance L between said first sensor g.sub.1 center
axis and said second sensor g.sub.2 center axis is such that a maximum
value of the sensor correlation function R.sub.g1g2, which adjoins the
intersection of the sensor correlation function R.sub.g1g2 derived from
the product of the sensor output characteristic curves with the abscissa,
lies on the ordinate.
To prevent the controller from locking on to another intersection with the
abscissa, in other words a false minimum value, in case of larger velocity
fluctuations, it is advantageous to make the distance L between the first
and second sensors g.sub.1, g.sub.2 such that the adjoining extreme point,
or maximum value, of the sensor correlation function R.sub.g1g2 lies on
the ordinate. By means of this it is possible from the start, beginning at
this extreme point, to "run up" the control loop circuit directly to the
intersection with the abscissa, or minimum value which corresponds to the
adjustment point.
A signal emitter g.sub.4 may be provided which transmits velocity signals
s.sub.4 which are approximately proportional to the yarn velocity, that
the signals s.sub.4 of the signal emitter g.sub.4 can be provided to the
transit time correlator for range preselection for the lock-on of the
control loop circuit on the real intersection of the cross-correlation
function .PHI.(.tau.) with the abscissa. A further possibility of
preventing the transit time correlator from locking on to a false minimum
value of the cross-correlation function .PHI.(.tau.), even with greater
velocity fluctuation, consists in using the additional signal emitter
g.sub.4, by means of which the controller is provided with a range
preselection for the range in which the adjustment point is located.
The invention will be described in detail below by means of exemplary
embodiments represented in the associated drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1a to e illustrate various sensor output characteristic curves of
sensors g.sub.1 and g.sub.2 with a plot of the associated sensor
correlation function R.sub.g1g2 ;
FIGS. 2a to e illustrate the associated sensors with the wiring of the
diode circuits;
FIG. 3a illustrates the sensor output characteristic curves of sensors
g.sub.1 to g.sub.3 ;
FIG. 3b represents a block wiring diagram for a transit time correlator for
utilization of the signals s.sub.1 (t) to s.sub.3 (1) generated by the
sensors g.sub.1 to g.sub.3 in accordance with FIG. 3a;
FIG. 4 illustrates a block wiring diagram for a transit time correlator
with an additional sensor g.sub.4 ; and
FIG. 5 is a graphic representation of cross-correlation functions depending
on the texture of the yarn.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to the drawings, and, more particularly, to FIGS. 1a to 1e,
examples of sensor output characteristic curves with the associated sensor
correlation function R.sub.g1g2 are illustrated graphically. A
particularly simple example is shown in FIG. 1a. In this case the sensors
g.sub.1 and g.sub.2 can be made by appropriately wiring first and second
photodiodes illustrated respectively at 1 and 2, in a manner as can be
seen in the associated FIG. 2a. In this case the signal s.sub.2 (t) of the
sensor g.sub.2 is directly derived from the first photodiode 1 output
signal, with the first photodiode 1 disposed upstream in relation to the
yarn running direction. It should be presumed that the yarn travel
direction is from left to right with respect to the figures. This standard
will hold true throughout the following discussion. The signal s.sub.1 (t)
of the sensor g.sub.1 is formed by means of an summation circuit 3,
wherein a negative signal coming from the first photodiode 1 is combined
with a positive signal coming from the second photodiode 2. The
designation b/2 represents a reference value for the width of a
photodiode.
The sensor correlation function R.sub.g1g2 is formed from the product of
the output characteristic curves of the sensors g.sub.1 and g.sub.2. The
distance between the sensors is defined as the distance of the effective
sensor center axes. With reference to the sensor arrangement in FIG. 2a,
the effective sensor center axis of the sensor g.sub.2 lies in the center
of the first photodiode 1, while the effective sensor center axis of the
sensor g.sub.1 lies at the separation line between the photodiodes 1 and
2. The distance L is therefore equal to 1/2 (b/2) or b/4.
As can be seen in FIG. 1a, the intersection of the sensor correlation
function R.sub.g1g2 with the abscissa, or the minimum value, is displaced
a distance L from the ordinate, or .epsilon.=L. The position of this
intersection point coincides with the intersection of the sensor output
characteristic curve of the sensor g.sub.1. In other words, the minimum
value of the sensor cross-correlation function is coincident with the
instantaneous zero value of the sensor output characteristic curve. To
obtain such a sensor output characteristic curve from the sensor g.sub.1,
the sensor must consist of two signal receivers, in this case the
photodiodes 1 and 2, disposed one behind the other in the running
direction of the yarn.
Since the effective sensor center axes form the basis for the definition of
the distance of the sensors from each other, which on the one hand is
based on the calculation of the model delay time .tau. as well as the
velocity, the intersection point of the sensor output characteristic curve
of the sensor g.sub.1 with the abscissa, or when the output value goes
through zero, in the effective sensor center axis is a prerequisite for
the intersection of the sensor correlation function R.sub.g1g2, as well as
the cross-correlation function .PHI.(.tau.), with the abscissa, indicating
minimum values for both functions. In this manner, this intersection can
be used directly, i.e. without any prior differentiation, for determining
the adjustment point for the model delay time (.tau.). In other words,
since the output characteristic curve of the sensor crosses a zero value
coincident with the minimum values for both the sensor correlation
function R.sub.g1g2 and the cross-correlation function .PHI.(.tau.),
differentiation is no longer required for determining the adjustment point
for the model delay time (.tau.) and time savings are realized with
respect to the calculation of yarn velocity.
Because of the point-symmetric behavior of the output characteristic curve
of the sensor g.sub.1 and the steady output characteristic curve waveform
of the sensor g.sub.2 in the area of the respective effective sensor
center axis in this area the sensor correlation function R.sub.g1g2 or the
cross-correlation function .PHI.(.tau.) also behave point-symmetrically.
This is a prerequisite for the suppression of systematic errors based on
the surface quality of the yarn when determining the adjustment point.
A variant of FIG. 1a is represented in FIG. 1b which differs from the first
variant in that the distance L has been increased from the value
illustrated in FIG. 1a. However, an additional expenditure is associated
with this because three photodiodes 4,5,6 must be employed.
The same sensor output characteristic curves were also used with the
variants shown in FIGS. 1c and d, but here again a different distance L
between the effective sensor center axes was selected. Accordingly, the
respectively required number of photodiodes 8,9,10,11,12,13,14,15,16,17,18
also changes in the associated FIGS. 2c and 2d.
It should be stressed that here the sensor output characteristic curve of
the sensor g.sub.2 also has a characteristic curve having a balanced
output. This is achieved using amplifiers 12,21, which double the signal
strength, as can be seen in FIGS. 2c and 2d. The result of this is that
the sensor signal from the sensor g.sub.2 s.sub.2 (t) is also free of mean
values. Because of that it is possible to omit a high-pass filter in the
signal path which would have to be used particularly if the signal should
be clipped prior to further processing.
Aside from the fact that in the variant shown in FIG. 1c and 2c only one
diode circuit with three photodiodes 8,9,10 is required, its minimum,
which is adjacent to the minimum value, or the intersection point of the
sensor correlation function R.sub.g1g2 with the abscissa, is located on
the ordinate, indicating a minimum output value greater than zero.
Accordingly, at the start of operations, the control loop circuit can be
"run up," starting at this minimum, as far as this intersection, because
of which a lock-on of the cross-correlation function .PHI.(.tau.) takes
place at the intersection with the abscissa corresponding to the
adjustment point.
A sensor correlation function which is broader than those discussed with
the previous examples results in connection with the embodiment
represented in FIG. 1e and 2e. While a narrower sensor correlation
function R.sub.g1g2 is more advantageous in regard to the scattering of
the estimated transit time data, the collecting range of the adjustment
point is greater, which has advantages in regard to the stability of the
control loop circuit. A broad sensor correlation function is of particular
advantage if the velocity greatly fluctuates during the time of measuring
and if the mean velocity is of interest.
It is possible to obtain the sensor output characteristic curves of the
sensors g.sub.1 and g.sub.2 of FIG. 1e using the diode circuit of the
photodiodes 22,23,24,25,26,27,28 of FIG. 2e. In this case only the
photodiode 25 is used for both sensors g.sub.1 and g.sub.2. However, it is
also possible to select the distance L to be equal to b/2, in which case
only five photodiodes would be required for the diode circuit, of which
the four photodiodes located downstream in the running direction of the
yarn would be respectively used in an analog manner for both sensors
g.sub.1 and g.sub.2. It may be appreciated that, the sensor signals
s.sub.1 and s.sub.2 here are also free of mean values due to the amplified
outputs of the sensor output characteristic curves.
Another embodiment of the present invention is represented in FIG. 3a by
means of the sensor output characteristic curves of sensors g.sub.1 to
g.sub.3. FIG. 3b illustrates the associated block wiring diagram for an
associated transit time correlator circuit.
The third sensor g.sub.3 is disposed in a manner wherein its output
characteristic curve agrees with that of the second sensor g.sub.2 and
sensor g.sub.3 is nonetheless arranged in a manner wherein its effective
sensor center axis coincides with that of the first sensor g.sub.1. In
this manner, the output characteristic curve of the sensor g.sub.3 is
displaced by an amount L in respect to the output characteristic curve of
the sensor g.sub.2.
The result of this is that the signal s.sub.2 (t), which is displaced by
the model delay time .tau.=T, of the second sensor g.sub.2 is identical
with the not-temporally-displaced signal s.sub.3 (t) from the third sensor
g.sub.3. The result in the case of .tau.=T therefore is the initial value
zero because of the different sign valuation at an addition point 32.
Therefore, a noise signal which may be present along with the signal
s.sub.1 (t) of the sensor g.sub.1 is eliminated as an input value of the
integrator 34. The scattering of the transit time estimate data therefore
disappears. The output signal .DELTA..tau. of the integrator 34 acting as
a feedback integrator is therefore also equal to zero. In this way and
with constant velocity, the delay time .tau. is not unnecessarily adjusted
in a delay circuit 31.
The controller output signal .DELTA..tau. is also transmitted to a dividing
element 35, whereby the value for .tau., by which the constant value L is
divided, is also readjusted there, if necessary. The respective
instantaneous value of the velocity is present at the output of the
dividing element 35.
An additional embodiment of the present invention is illustrated with a
block wiring diagram in FIG. 4. There, a sensor g.sub.4 is employed which
generates an output signal sequence s.sub.4 (t). Although a sensor g.sub.3
is not included here, it could also be employed. The sensor g.sub.4 is
essentially a pulse sensor 40, by means of which pulses are received from
a drive drum 41 for a bobbin 43. For example, and as will be appreciated
by those skilled in the art, the drive drum 41 can have a field spider to
which stationary Hall sensors are assigned. Thereby, a number of pulses
corresponding to the number of poles of the field spider are generated
during a revolution of the drive drum 41. This signal sequence s.sub.4 (t)
is counted in a counter 44. The time-dependent counting results are then
issued to a digital range comparator 45 which is supplied with the
controller output signal .DELTA..tau. from the output of the integrator
46. The output of the range comparator 45 is connected with the integrator
46, in which a range preselection for the position of the adjustment point
takes place. Therefore, it is possible to effectively prevent the control
loop circuit from locking on an intersection of the cross-correlation
function .PHI.(.tau.) with the abscissa, or minimum value thereof, which
does not correspond to the sought adjustment point. It is possible to
additionally supply this range comparator 45 with an offset entry
capability, not shown here, by means of which the width of the range can
be set.
Although the signal of the sensor g.sub.4 is not very exact due to the
slippage between the drive drum 41 and the bobbin 43, it is sufficient for
a range preselection for the integrator of the transit time correlator. In
this manner, the correct adjustment point is immediately found with
practically no increase in computing capacity requirements, even at higher
velocity changes.
In the example in accordance with FIG. 4 the analog signals s.sub.2 and
s.sub.1 are digitized by triggers 36 and 38, and are quantized to one bit.
The computing outlay is small, so that an 8-bit micro-controller is
sufficient for adjusting the pattern transit time .tau.. Accordingly, the
integrator 46, the range comparator 45, the delay member 37 and the
multiplier 39 have been replaced by digital components. For example, the
delay member 37 can be replaced by a shift register, while the multiplier
39 is a phase detector. A dividing element 47 and a further integrator 48
are also digital.
From the start of winding of a bobbin, the yarn length wound on the bobbin
tube is cumulatively determined in the integrator 48 on the basis of the
velocity and the winding time. In this way it is possible to determine the
yarn length wound on the bobbins with heretofore unrealized accuracy.
FIG. 5 illustrates a plot of cross-correlation functions generated in
accordance with the sensor output characteristic curves and sensor
arrangements according to the present invention. It can be seen here that
the slope of the cross-correlation function changes with the bandwidth of
the texture of the yarn (critical frequency f.sub.1 <f.sub.2 <f.sub.3).
This dependence of the slope of the cross-correlation function, however,
is considerably less than with the transit time correlation using the
differentiated correlation function. This has very positive effects on the
stability of the control loop circuit in respect to variable textures,
because the changes of the slope of the cross-correlation function
directly result in a proportional change of the loop amplification of the
adjustment control loop circuit.
It will therefore be readily understood by those persons skilled in the art
that the present invention is susceptible of a broad utility and
application. Many embodiments and adaptations of the present invention
other than those herein described, as well as many variations,
modifications and equivalent arrangements, will be apparent from or
reasonably suggested by the present invention and the foregoing
description thereof, without departing from the substance or scope of the
present invention. Accordingly, while the present invention has been
described herein in detail in relation to its preferred embodiment, it is
to be understood that this disclosure is only illustrative and exemplary
of the present invention and is made merely for purposes of providing a
full and enabling disclosure of the invention. The foregoing disclosure is
not intended or to be construed to limit the present invention or
otherwise to exclude any such other embodiments, adaptations, variations,
modifications and equivalent arrangements, the present invention being
limited only by the claims appended hereto and the equivalents thereof.
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